Replacement cathode assembly

ABSTRACT

A replaceable electron emission cathode for use in electron guns within television picture tubes or the like. The first grid of an electron gun forms a support member for an electron emission cathode assembly which is held to the support member by retainer means. The support member has a plurality of spaced-apart severable tablike portions extending therefrom to mate with and be fastened to corresponding tablike portions formed on the retainer means. To replace the cathode of the electron gun, the fastened together tablike portions of the support member and retainer means are severed from the structure to allow removal of the retainer means and cathode assembly. A new cathode assembly is inserted and held in place by the same or new retainer having other or new tablike portions mating with and are fastened to auxiliary ones of the tablike portions on the support member.

2,432,789 12/1947 OLarte et a1 lnventor Donald A. Nels Lombard, llll.

Appl. No. 1,760

Filed Jan. 9, 1970 Patented Assignee Aug. 24, 1971 Motorola, Inc. Franklin Par-lg lll.

REPLACEMENT CATHODIE ASSEMBLY 3,114,068 12/1963 Shortridge .4 3,176,179 3/1965 Kuehneetal AIBSTRAQT: A replaceable electron emission cathode for use in electron guns within television picture tubes or the like. The first grid of an electron gun forms a support member for an electron emission cathode assembly which is held to the support member by retainer means. The support member has a pluralityof spaced-apart severable tablike portions extending therefrom to mate with and be fastened to corresponding tablike portions formed on the retainer means. To replace the cathode of the electron gun, the fastened together tablike portions of the support member and retainer means are severed from the structure to allow removal of the retainer means and cathode assembly. A new cathode assembly is inserted and held in place by the same or new retainer having other or new tablike portions mating with and are fastened to auxiliary ones of the tablike portions on the support member.

PATENTED M1824 1971 FIG. 2

Inventor DONALD A. NEIS ,MMW

ATTYS.

REPLACEMENT CATHODE ASSEMBLY BACKGROUND OF THE INVENTION This invention relates generally to electron discharge devices, and more particularly to a cathode support structure which allows simple removal of the cathode for replacement thereof when such electron discharge devices are being rebuilt.

Electron beam devices, such as the type used to form electron guns in television picture tubes, are very complex, intricate and expensive structures having a multitude of interrelated components which are critically spaced from one another to provide optimum efficiency and performance of such electron devices. These electron discharge devices, as well as the television picture tubes incorporating the same, are relatively expensive and it is worthwhile to dismantle old picture tubes and the electron guns therein and rebuild them to a like-new condition so they will again provide many years of service.

In the case of electron guns use in television picture tubes, great difficulty arises when trying to replace the cathode element of the electron gun without disturbing the geometrical spatial relationship between various grid components of the electron gun. Since the cathode element, in most cases, is mounted within a cylinderlike grid element by means of a disclike member of dielectric material which serves also to insulate the cathode and grid element, it is very difficult, if not impossible, to remove the cathode element without also removing the associated grid element, or at least in some manner bending it out of shape, which is an undesirable result.

Since the cost of rebuilding these electron guns and picture tubes must be maintained below the cost of manufacturing new ones, it is desired to salvage as many components as possible, and to make the necessary replacements of components in a minimum of time. This is particularly true in the case of multigun devices, such as a tribeam electron gun used in color television sets. The trigun arrangement within color picture tubes is substantially three electron guns nestled closely together. Each of these guns has its own separate cathode and grid elements and, therefore, upon rebuilding such electron guns the problems encountered are triplicated. Also, because of the relative size of the trigun assembly, they being relatively small as compared to a single electron gun arrangement within a black and white picture tube, it is relatively difficult to remove the old cathodes from the guns without inflicting further unnecessary damage thereto which may result in damaging the gun beyond repair.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a cathode support structure for electron discharge devices which overcomes many of the problems of rebuilding the same, and which is inexpensive to manufacture, reliable and efiicient in operation, and which allows cathode replacement in a minimum of time.

Another object of this invention is to provide a cathode and support grid structure which allows rebuilding of the associated electron gun more than once without replacing the support grid.

Yet another object of this invention is to provide a cathode structure and mounting means therefor which can be made small in size for use in trigun picture tubes and to be readily replaceable when rebuilding trigun electron discharge devices used therein.

Briefly, an electron discharge device is constructed in accordance with the principles of this invention by providing a support member for receiving and holding electron emission cathode means in a fixed position relative to the support member by the use of severable tabs or the like which can be cut or broken loose to allow removal of the cathode. The support member preferably is a cylindrical grid element being fully open at the rear of the grid element to receive the cathode assembly. The cylindrical grid element has a plurality of spaced-apart tablike members extending axially rearwardly thereof. Preferably the tablike members are formed in diametrically opposed pairs, there being, for example, three pairs of tablike members disclosed in the illustrated embodiment. The cathode is formed of a cylindrical sleeve of a lesser diameter than the inner diameter cylindrical grid and includes a support ring of dielectric material extending radially outwardly of the cylindrical sleeve and is sized to fit snugly within cylindrical grid element.

Most advantageously, a retainer having at least two tablike portions is inserted into the cylindrical grid firmly to hold the cathode assembly in a substantially fixed position therein. The tablike members of the retainer are arranged in mating relation with a selective pair of tablike members of the cylindrical grid and fastened thereto by spot-welding, or the like, only through the limited area provided by the axially extended tablike portions. If it becomes necessary to rebuild the electron gun and picture tube using the cathode assembly of this invention, the previously fastened together tablike portions are severed, such as by breaking or cutting the same, and the retainer and cathode structure are then easily removed from within the cylindrical grid which was supporting the cathode assembly. A new cathode assembly and support ring are inserted into the cylindrical grid and a new retainer is inserted behind the cathode but with the tablike portions thereof in mating relation with a second pair of tablike portions on the cylindrical grid. The newly mated pairs of tablike portions are then fastened together by spot-welding, or the like, and the electron gun has been rebuilt quickly and easily by replacing the cathode therein.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary partial sectional view of the neck portion of a color television picture tube illustrating a trigun electron discharge device therein with portions thereof broken away for clarity;

FIG. 2 is a rear view of a cylindrical grid and the retainer used therein for holding a removable cathode structure in accordance with this invention;

FIG. 3 is a side sectional view taken along section line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERREDEMBODIMENT Referring now to the drawings, wherein like reference numerals throughout the various views of the drawings are intended to designate similar elements or components, there is seen 'a cylindrical grid and cathode structure designated by reference number 10, which is one of three such grid and cathode structures of a trigun electron discharge device 12 mounted within a neck 14 of a color television picture tube. The neck portion 14 is sealed by a glass stem member 16 positioned at the end of neck 14, and through which a plurality of pins or counterleads 18exte nd and are supported therein. The pins 18 provide meansfor connecting various electrodes of the electron gun assembly 12 to the appropriate circuitry within the television receiver. The various details of construction of the trigun assembly 12, except for the novel arrangement of the grid and cathode structure 10, may be of conventional design as is well known in the art and, therefore, it is not necessary to describe the well-known arrangements of these components.

However, in accordance with this invention, the grid and cathode assembly 10 provide a novel arrangement whereby the cathode thereof is readily replaceable with a minimum of time and expense and without disturbing the spatial relationship between the various grid components of the trigun device 12. Although this invention is herein illustrated in connection with use in a trigun electron discharge device, it will be understood that it can be used to equal advantage in connection with single gun electron beam devices such as those provided in black and white picture tubes.

For a better understanding of the novel features of this invention reference should now be made to FIGS. 2 and 3 wherein the grid-cathode assembly is illustrated in full detail. The cylindrical grid member has one end 22 thereof substantially closed off except for a small aperture 24 through which electrons flow ultimately to impinge uponth e rear surface of the television picture tube associated therewith. The cylindrical grid member 20 has the other end 26, this being referred to as the rear end, fully open to provide access for a cathode structure 28 and a retainer 30. 7

Most advantageously, a plurality of spaced-apart tablike members 31 extend longitudinally of the cylindrical grid member 20 and are directed rearwardly thereof to provide selective surfaces to receive spot-welds, or the like, to hold the grid and cathode in an assembled condition. The cathode member 28 includes a sleeve member 32 having a deposit 34 of electron emissive material formed at one end thereof to be closely spaced to the aperture 24. A heatmgelement 36 is positioned within the sleeve 32 to heat the deposit 34 of electron emissive material and boil off electrons therefrom in the conventional manner. A support ring 38 extends radially outwardly of the sleeve 32 to abut with a stop flange or ring 40 which may be formed or fastened within the cylindrical grid 20, or merely positioned therein and held in place by the cathode structure 28 and retainer 30. Also, the stop ring 40 may be eliminated and an annular restriction formed within the cylindrical grid member, if desired. Preferably, the retainer includes at least a pair of diametrically opposed tablike members 42 which are arranged to mate with a corresponding pair of diametrically opposed tablike members 31 of the cylindrical grid member 20. The number of tablike members 31 is unlimited except from a practical standpoint as to the number of tabs that can be placed around the grid member 20. The mating tabs 31 and 42 are fastened together as by spot welding, or the like, and the initial construction of the grid and cathode assembly 10 is completed. An electrode connection 44 is provided on the outer surface of the cylindrical grid 20 to electrically couple the same to the appropriate pin 18 extending from the neck 14. Similarly, an electrode connection 46 is made with the sleeve 32 of the cathode member 20 for electrically coupling the same to the appropriate pin 18 of the picture tube, and electrode connections 48 and 49 are provided at the heater 36 for applying energizing voltage thereto.

After the picture tube has been in service for some time, for example several years or more, it may be necessary as well as advantageous to dismantle the picture tube and rebuild the same and to rebuild the trigun assembly 12. Most often, the only element necessary to be replaced when rebuilding electron guns of television picture tubes is that of the cathode member 28 because of the depletion of the deposit 34 of electron emissive material formed thereon. By replacing the cathode structure 28 a new quantity of the deposited electron emissive material is introduced into the electron gun thus revitalizing the gun for another long period of use.

To remove the old cathode structure 28 the previously welded together tab members 31 and 42 are severed from the cylindrical grid 20 and retainer 30, respectively, in the approximate vicinity of the notched out portions 50. The severing of these fastened together tablike portions loosens the retainer 30 and allows removal thereof to gain access to the cathode structure 28. The cathode structure 28 is also removed with minimum effort and time.

A new cathode structure is inserted into the cylindrical grid member 20 followed preferably by a new retainer 30. The extended tablike portions of the new retainer are then placed in mating relation with one of the remaining diametrically opposed pairs of tablike portions 31 and fastened thereto by spot welding, or the like. This simple and unique cylindrical grid and retainer structure enables quick and economical replacement of the cathode structure 28. Although the retainer 30 is herein illustrated as having only a pair of diametrically opposed tablike members 42 it would be understood that a retainer having as many tablike portionsas are formed on the cylindrical grid member 20 can be provided, it being understood that only selected pairs 'of the mating tabs will be fastened together by welding during any given instance. Therefore when removing the retainer so formed and replacing the cathode structure within the cylindrical grid the retainer can be replaced and fastened in position by using a next pair of tablike members. Therefore, by using the novel structural arrangement of the 'disclosed cylindrical grid member and retainer to hold a cathode structure firmly in position within the cylindrical grid, the cathode structure can bereadily removed by severing previously welded together tablike portions and removing the retainer and cathode member, and replacing the cathode structure with a new one.

I claim: 1. An electron discharge device having a support member for receiving and holding a first electron emission cathode means, comprising in combination: first and second pairs of spaced-apart severable tab means formed on said supportmember to be spaced from said first cathode means;

retainer means engaged with said first cathode means to hold said first cathode means in a substantially fixed position relative to said support member, said retainer means having mating tab means formed thereon to mate with and be fastened to said'first pair ofspaced-apart severable tab means for holding said first cathode means and said retainer means in an assembled relation, said second: pair of spaced-apart severable tab means being available to hold a second cathode means on said support member upon removal of said first cathode means.

2. The electron discharge device of claim v1 further including stop means formed on said support member for receiving a portion of said first cathode means abutted thereagainst, said first cathode means being positioned between said stop means and said retainer means and held in position on said support member by the fastened together tab means.

3. The electron discharge device of claim 1 wherein said support member is a cylindrical sleeve forming a grid of the electron discharge device, said cylindrical sleeve having rearwardly, axially extending portions forming said first and second pairs of spaced-apart severable tab means, said first cathode means mounted within said cylindrical sleeve,.and

said retainer means being an annular ring with turned back portions at the periphery thereof to mate with and be fastened to said first pair of the tab means on said cylindrical sleeve to hold said first cathode means and said cylindrical sleeve in an assembled condition.

4. The electron discharge device of claim 1 wherein said support member is a cylindrical sleeve forming a grid of the electron discharge device, said first cathode means includes a second cylindrical sleeve of lesser diameter than said cylindrical sleeve forming said grid and inserted therein, said first cathode means having a radially extending spacer member of dielectric material which engages stop means formed within said cylindrical sleeve forming said grid, and said retainer means is an annular ring having turned back portions at the periphery thereof to mate with and be fastened to said first pair of the tab means formed on said cylindrical sleeve forming said grid to hold said grid and said cathode means in an assembled condition.

5. The electron discharge device of claim 4 wherein saidcylindrical sleeve forming said grid and said first cathode means form components of an electron gun arranged for insertion into a television picture tube.

6. The electron discharge device of claim 5 wherein the electron gun formed by said cylindrical sleeve forming said grid and said cathode means is a tribeam electron gun arranged for insertion into a color television picture tube. 

1. An electron discharge device having a support member for receiving and holding a first electron emission cathode means, comprising in combination: first and second pairs of spaced-apart severable tab means formed on said support member to be spaced from said first cathode means; retainer means engaged with said first cathode means to hold said first cathode means in a substantially fixed position relative to said support member, said retainer means having mating tab means formed thereon to mate with and be fastened to said first pair of spaced-apart severable tab means for holding said first cathode means and said retainer means in an assembled relation, said second pair of spaced-apart severable tab means being available to hold a second cathode means on said support member upon removal of said first cathode means.
 2. The electron discharge device of claim 1 further including stop means formed on said support member for receiving a portion of said first cathode means abutted thereagainst, said first cathode means being positioned between said stop means and said retainer means and held in position on said support member by the fastened together tab means.
 3. The electron discharge device of claim 1 wherein said support member is a cylindrical sleeve forming a grid of the electron discharge device, said cylindrical sleeve having rearwardly, axially extending portions forming said first and second pairs of spaced-apart severable tab means, said first cathode means mounted within said cylindrical sleeve, and said retainer means being an annular ring with turned back portions at the periphery thereof to mate with and be fastened to said first pair of the tab means on said cyLindrical sleeve to hold said first cathode means and said cylindrical sleeve in an assembled condition.
 4. The electron discharge device of claim 1 wherein said support member is a cylindrical sleeve forming a grid of the electron discharge device, said first cathode means includes a second cylindrical sleeve of lesser diameter than said cylindrical sleeve forming said grid and inserted therein, said first cathode means having a radially extending spacer member of dielectric material which engages stop means formed within said cylindrical sleeve forming said grid, and said retainer means is an annular ring having turned back portions at the periphery thereof to mate with and be fastened to said first pair of the tab means formed on said cylindrical sleeve forming said grid to hold said grid and said cathode means in an assembled condition.
 5. The electron discharge device of claim 4 wherein said cylindrical sleeve forming said grid and said first cathode means form components of an electron gun arranged for insertion into a television picture tube.
 6. The electron discharge device of claim 5 wherein the electron gun formed by said cylindrical sleeve forming said grid and said cathode means is a tribeam electron gun arranged for insertion into a color television picture tube. 